Severe aortic stenosis (AS) is a serious medical condition that can ultimately lead to death, but is often left untreated because of high perioperative surgical risk. As a result, transcatheter aortic valve replacement (TAVR) therapy has emerged as a percutaneous approach for prosthetic aortic valve delivery for the treatment of AS. Complications following TAVR are related to paravalvular leakage, which has been linked in part to inaccurate prosthetic valve size selection compared to the true native aortic annulus size. Although imaging modalities are used to assess aortic valve annulus size prior to TAVR, these methods are subjective, can be inaccurate, and also add additional time, cost, and clinical procedures. Since it is standard procedure to perform valvuloplasty just prior to valve deployment, annular sizing information can be obtained from the valvuloplasty balloon and used to select the proper valve size. The pressure/diameter relationship of the balloon could be useful here, however, non-uniform balloon expansion makes sizing of the aortic valve annulus difficult for semi-compliant valvuloplasty balloons. Consequently, we have developed a novel sizing valvuloplasty conductance balloon (SVCB) catheter system that functions as a typical valvuloplasty balloon catheter, but with additional functionality for accurate display of real-time balloon size for aortic annulus assessment using electrical conductance measurements. This is unlike other systems that rely on standard pressure/diameter relationships to acquire balloon size across the entire balloon. Rather our system uses an electrical law of physics to obtain precise annular dimension despite any asymmetries that could arise in the balloon dimension during inflation. The sizing results are displayed in real-time on a simple bed-side console display to aid the physician during balloon expansion (i.e., similar to current displays that show pressure during inflation). The preliminary results with our SVCB catheter system on the bench and in healthy swine showed excellent accuracy (2% diameter error), as was the repeatability (<1% diameter error), and safety (no arrhythmias or death). However, additional work is needed to refine the console and catheter and to further validate the system in diseased swine (this Phase I application) before translation to man (future Phase II application). Therefore, in this Phase I application, we propose the creation of a clinically ready SVCB catheter system and its validation in vivo in diseased swine. Based on the physics foundation of the technology and the excellent preliminary sizing and safety results, the SVCB catheter system is expected to provide highly accurate and repeatable real-time digital display of aortic annulus size with virtually no physician training required. This project has the ability to impact patients with multiple comorbidities and reach across various NIH Institutes and Centers including the NHLBI and NINDS.